I. Field of the Invention
This invention relates generally to an apparatus for processing image data, and more specifically to an apparatus for processing image data of a computerized tomography (CT) system in order to construct tomographic images.
II. Background Information
The conventional CT system as disclosed, for example, in U.S. Pat. No. 4,135,247 to Gordon et al. includes a CT scanner comprising a radiation (e.g., x-ray) source, and radiation detectors for scanning an object to collect image data. The radiation source of the CT scanner is rotated about the object. The radiation source generates radiation (e.g., X-ray) beams which are directed toward the object. As the radiation source is rotated about the object, the radiation beams pass through the object at points along one-dimensional lines or slices of the object and emerge from the object at intensities which vary according to the composition of the object at the points through which the radiation beams are passed. The radiation detectors are positioned opposite the radiation source to detect beams emerging from the object. The radiation source and the radiation detectors are arranged to scan the object by rotating the radiation source at least 180.degree. around the object. The radiation detectors detect beams for the complete 180.degree. range of rotation of the radiation source and for fan beams beyond the range of rotation of the radiation source. (In an alternative arrangement, the CT scanner may include a single radiation detector which rotates around the object opposite the radiation source to detect emerging radiation beams.)
Each radiation detector is a discrete element having a current output which corresponds in magnitude to the intensity of the X-ray beam emerging from the object at a given angle and incident on the radiation detector.
The current outputs of the radiation detectors for radiation beams emerging from the object at given angles comprise image data of the CT scanner for the points along the one-dimensional lines or slices of the object about which the source is rotated. The image data for the object, as collected by the CT scanner, is in analog form.
The conventional CT system further comprises a converter and an image data processor. The converter first LOG converts (or LOG amplifies) the image data of the CT scanner, then converts the image data from analog form to digital form. After the image data has been LOG converted and put in digital form, the image data is provided to the image data processor.
The image data processor processes the image data to construct a tomographic image of the object irradiated by the radiation source of the CT scanner. The image data processor includes a corrector, a convolver, and a back projector. The corrector utilizes correction data obtained by taking image data for well known phantom objects (as, for example, water) to correct converted image data. The correction data enables the corrector to determine and compensate for the nonuniform sensitivity of the radiation detectors. The corrected image data is supplied to the convolver. The corrected image data is convolved in accordance with a specific filter function to ensure that the constructed tomographic image is not blurred. The image data, having been corrected and convolved by the image processor, is subsequently back projected by the image data processor. Convolved image data is supplied to the back projector which has an image memory for storing image data for a one-dimensional line of image data obtained by the CT scanner. The convolved image data for a one-dimensional line is back projected according to the location of points along the one dimensional line from where the image data was collected, and according to the angle of rotation of the radiation source utilized in obtaining image data for each of the points along the one-dimensional line. The back projected data is stored in the image memory according to the location of points and the given angles of rotation.
The image processor of a conventional CT system performs the correction, convolution and back projection of image data at relatively high speed. Each of the steps of correction, convolution and back projection are performed by separate hardware units which are arranged in a pipeline processor arrangement in accordance with the sequence of processing steps to be performed.
The hardware units of the conventional CT system image processor can perform, however, only a single designated processing function, such as correction, convolution or back projection. Processing of image data is therefore limited, for systems not having a variety of hardware units, to only those single processing functions performed by each hardware unit of the CT system. For example, the conventional CT system having a corrector, convolver, and back projector cannot perform overlapping and magnification. To accomplish these additional operations, additional hardware units are required.
Further, the hardware units are arranged in a pipeline processor arrangement and data flows only one way through the pipeline-arranged hardware units, with processed image data being stored at the end of the pipeline only. Functional checks of the output from each of the processing hardware units cannot be performed while the CT system image processor is being operated.
Accordingly, an object of the present invention is to provide an apparatus for processing image data of a CT system which utilizes basic operation circuits which are arranged in parallel, and which are interconnected under the control of a program to other basic operation circuits to perform different processing functions.
Another object of the present invention is to provide an apparatus for processing image data of a CT system which may perform functional checks on the operation of each operation circuit of the image data processing apparatus.
Yet another object of the present invention is to provide an apparatus for processing image data of a CT system to which additional operation circuits may be added in parallel to increase the processing capability of the image data processing apparatus.
Another object of the present invention is, further, to provide an apparatus for processing image data of a CT system which includes a process controller for controlling the transfer of data between memories to minimize transfer loss.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description or may be learned by practice of the invention.